/Engine/Source/Runtime/Experimental/Chaos/Public/Chaos/XPBDStretchBiasElementConstraints.h
Stiffness is in kg cm / s^2 for stretch, kg cm^2 / s^2 for Bias.
static constexpr [FSolverReal](API\Runtime\Chaos\Chaos\FSolverReal) MinStiffness = (FSolverReal)1e-4;